Piston construction



June 1941- R. M. HAZEN ETAL 2,244,008

' PISTON CONSTRUCTION I Filed June 16, 1939 4 WELD v m U u Patented June 3, 1941 2,244,003 PISTON cons'mucrron Ronald M. Hanan and Thomas s. Mcbrac, Jr... En-

dianapolis, Ind, assignor to General Motors Corporation, Detroit, Mich, a corporation oil Delaware Application June is, 1939, Serial No. 279,410

I 5 Claims.

This invention relates to pistons and especially to light alloy pistons for high-speed engines, and is a continuation in part of the parent Patent No. 2,159,989 of May 30, 1939.

It relates particularly to such pistons for use in internal combustion engines.

In modern high-speed two-cycle engines, the conditions under which the pistons have to operate are particularly severe. Other things being equal, the specific output of a two-cycle engine is twice that of a four-cycle engine and there is approximately twice the waste heat to be dissipated through the parts in a given time. The

high thermal conditions not only frequently cause difflculties due to ring sticking, but decrease the strength of the piston to the point where failure may occur.

I Accordingly, it is becoming increasingly important to provide pistons which are light, but of adequate strength, while capable of dissipating effectively the heat to which they are subjected.

, The objectof the invention is a strong, light weight piston, capable of quickly dissipating the heat to which it is subjected.

Another object oi! the invention is a piston in which the heat flow to the ring belt is limited. It is a further object of the invention to achieve the foregoing objects in a piston which can be simply and cheaply produced.

The above and other objects of the invention will be apparent as the description proceeds.

According to the invention, the crown of the piston is supported from the piston pin. bosses mainly by a circular strut forming an inner wall,

spaced from and .of greater section than the outer wall of the piston and providing an annular insulating air space between the two walls. The piston is made in separate pieces subsequently fastened together by screwed and/or welded joints, or the, like. One of said pieces forms a part of the wall of the annular insulating air space and includes the crown, the strut and the bosses, and there is a joint between this pieceand the-remainder oi the piston, in the outer periphery oi the piston above the piston pin bosses.

The built up construction permits of greater control and freedomwin the-choice of section and in the provision at suitable cooling fins and insulating air spaces.

' The drawing shows three modifications of a piston according to the invention.

Fig. l is a view, partly in elevation and partly a in section, of a piston structure according the invention.

(01. soc-14) Fig. 2 is a view partly in elevation and partly in section of a modification according to the invention.

Fig. 3 is a partsectlonal view on line 3-3 of Fig. 1.

Fig. 4 is -a part sectional view on line 4-4 of Fig.2.

Fig. 5 is a part elevational and part sectional view of another modification according to the invention.

In all the structures illustrated, the piston is provided with diametrically opposite bosses such as i, having bearings 2, for a piston pin (not shown). Integral with the bosses i, is the piston crown 3, supported from the bosses by a circular strut l and cooling and strengthening fins 5. The circular strut 4 forms the inner'wall of an annular insulating air space 6 between the strut l and the ring beit area of the piston which is between the crown and the piston pin bosses. The ring belt area is formed separately from the piece including the crown. the strut and the bosses and is provided with grooves for conventional packing rings (not shown). In Figs. 1 and 3, the piston skirt 8 is integral with the piston crown, thestrut and the bosses. The ring belt area consists of'two semicircular pieces 9 and III, which when in position on the piston, are welded to each other, and to the remainder of the piston, at the peripheral rim ll of the crown, and the edge 0! the skirt 8 at a point above the bosses.

InFigs. 2 and 4, the ring belt area and the piston skirt together, are formed in two semicircular pieces I4, and I5. Each of the pieces ll and I! has a bore such as It. in which one of the diametrically opposite bosses such as l and its bearing, such' as 2 are spigoted. when in position on the piston, the .two semicircular pieces II and I! "are welded to each other, and to the remainder of the piston, at the peripheral rirn I6 0! the'crown.

In Fig. 5, the piston skirt i1 is integral with the piston crown, the strut and the bosses. The ring belt area consists oi. a ring ll, whichhas female threads. l9 engaging male threads 20 on the piston crown. The piston structure is completed by screwing the two parts together, after which the threaded Joint between the ring I! and the crown is sealed and the joint between the ring l8 and the top edge of the piston skirt above the bosses is sealed, by welding as indicated.

In all the examples illustrated, the annular space extends closento the outer cylindrical surface of the pistonjat mints above and below the ring belt area in the outer wall of the piston and has at all points a greater cross-sectional area than points above and below the ring belt area. The heat flow from the head of the piston to the ring belt area is restricted by the narrow section of metal between these two parts. The circular strut forming the inner wall of the insulating annular space is sufflciently large to carry the main gas pressure loads and the' heat flow directly on to the piston pin bosses-only a small part of the load and the heat flow being transmitted through the outer section of the piston.

Because of the lower temperature of-the ring belt area, due to the lessened heat flow to this part, the possibility of piston rings sticking, consequent on carbonization of the lubricating oil at the temperature which would otherwise exist, is avoided.

The parts of the piston can be made of any suitable light alloy (either forged or cast), and it will be seen that a structure has been provided in which all critical points, as well as the cooling fins, may be completely machined to any desired tolerance limits before assembly.

We claim:

1. In a piston having a crown, a skirt, piston pin bosses, and a ring belt area in the outer wall of the piston between the crown and the piston pin bwses, a strut to support the crown from the piston pin bosses and forming an inner wall spaced from the outer wall of the piston to provide an enclosed annular insulating air space between the ring belt area and the strut forming the inner wall, said inner wall having at all points in its circumference a greater cross-sectional area than the cross-sectional area at points in its circumference above and below the ring belt area in the outer wall of the piston, whereby only small portions of the gas pressure loads and the heat to which the crown is exposed in.- an engine cylinder, are transmitted to the ring belt area, and the main portions or the gas pressure loads and the heat flow, are carried directly through thelinner wall to the piston pin bosses, said piston consisting of a plurality of pieces fastened together, one of said pieces forming a part of the wall of the annular insulating air space and including the crown, the strut, and the bosses, there being a joint in the outer periphery of the piston above the piston pin bosses, between said piece and the remainder of the piston including the ring belt area.

2. The combination according to claim 1, in which the piece including the crown includes the skirt.

3. The combination according to claim 1. in which the piece including the crown includes the skirt, and the ring belt area is formed of two semicircular pieces secured together and to the piece including the crown.

4. The combination according to claim 1, in

which the ring belt area and the skirt together, consist of two semicircular pieces secured together and to the piece including the crown. 5. The combination according to claim 1, in which the piston is a two-piece piston in which the piece including the crown includes the skirt. and the ring belt area is formed in the other piece.

RONALD M. HAZEN. THOMAS S. McCRAE, JR. 

